In the manufacture of pressure-sensitive recording papers, better known as carbonless copy papers, a layer of pressure-rupturable microcapsules containing a solution of colorless dyestuff precursor is normally coated on the back side of the front sheet of paper of a carbonless copy paper set. This coated backside is known as the CB coating. In order to develop an image or copy, the CB coating must be mated with a paper containing a coating of suitable color developer, also known as dyestuff acceptor, on its front. This coated front color developer coating is called the CF coating. The color developer is a material, usually acidic, capable of forming the color of the dyestuff by reaction with the dyestuff precursor. Marking of the pressure-sensitive recording papers is effected by rupturing the capsules in the CB coating by means of pressure to cause the dyestuff precursor solution to be exuded onto the front of the mated sheet below it. The colorless or slightly colored dyestuff, or dyestuff precursor, then reacts with the color developer in the areas at which pressure was applied, thereby affecting the colored marking. Such mechanism or the producing technique of pressure-sensitive recording papers is well known.
Among the well known color developers used on CF record sheets are phenolic-type resins, such as acetylated phenolic resins, salicylic acid modified phenolics and, particularly, novolac type phenolic resins.
Among the well known basic, reactive, colorless, chromogenic dye-precursors useful for developing colored marks when and where applied to a receiving sheet coated with such color developers are Crystal Violet Lactone (CVL), the p-toluenesulfinate salt of Michler's Hydrol or 4,4'bis(diethylamino)benzhydrol, Benzoyl Leuco Methylene Blue (BLMB), Indolyl Red, Malachite Green Lactone, 8'-methoxybenzoindoline spiro-pyran, Rhodamine Lactone, and mixtures thereof.
Acid sensitized record receiving sheets have previously been prepared by application of an aqueous slurry of finely ground resin to a paper substrate, as is disclosed, for example, in U.S. Pat. No. 3,672,935. It is also known to apply the resin to the substrate paper sheet as a solution in a volatile organic solvent which evaporates completely after application to leave a thin film of solid resin on the sheet. The latter method is taught in U.S. Pat. Nos. 3,466,184 and 3,466,185. The consistency of these solid solutions and the necessarily volatile solvents used therein give rise to printing problems, causing swelling of rubber plates and rolls. Furthermore they have high energy requirements and environmental contamination problems. The above discussed aqueous slurry application has high energy requirements in grinding the resin and in drying the applied slurry. Such slurries are also not adaptable to printing techniques. Very often, the film of phenolic resin which has been applied to the paper does not adhere firmly to the paper which can cause dusting and offsetting during printing operations.
One previous solution to the problem of standard printing operation adaptability is illustrated in U.S. Pat. No. 4,060,262. The present invention, by the same inventor, is essentially an improvement over said patent.